sodininkystė ir daržininkystė 25(4)

Effect like induction of adventitious root formation is typical for auxin group
phytohormones as it was found in experiments of Jun Chen et al. (1995) with soybeans
cuttings, treated with NAA. Adventitious root formation was induced by NAA
between 10 and 500 µM showed the optimum root number at 500 µM followed by
inhibition at 1 000 µM and higher concentrations of NAA. Similar results were also
reported by Zin-Huang et al. (1998), when adventitious root formation was particularly
enhanced by exogenously applied auxins and polyamines. IBA promoted the
soybean hypocotyls rooting in vitro more than NAA did. It could be explained as the
exogenously applied auxin (IBA or NAA) acts on polyamine synthase and IAA oxidase
at the gene level or through enzyme regulation (Zin-Huang et al., 1998).
Chlorophyll fluorescence, emitted from PSII responds to large number of different
environmental factors and reflects the physiological state of higher plants and
algae. Fluorescence measurements are based on the principle by which light quantum,
captured by chlorophyll of light-harvesting complex is transferred to chlorophyll
P680 in PSII RC and via electron transport chain between both photosystems
produces photochemical work. Otherwise it can be dissipated non-photochemically
as heat or fluorescence. As described by Kitajima and Butler (1975) these processes
can be considered as competing first order reactions with rate constants for fluorescence,
thermal dissipation and photochemistry. Increased flow of the excitation energy
into a photochemical pathway leads to a decrease (quenching) of the chlorophyll
fluorescence yield. In this way chlorophyll fluorescence reflects changes in the efficiency
of photosynthetic processes (Schreiber et al., 1995; Weis and Lechtenberg,
1989; Govindjee, 1995). Exploring the influence of phytohormones on photosynthesis
the most reported effect is stomata regulation, also protective mechanism in the
stress conditions. However, the scientific literature contains more evidence that phytohormones
can regulate other processes of photosynthesis. For instance, Pandey et
al. (2000) reported in the experiment of hormonal regulation of photosynthetic enzymes
in cotton under water stress reported that all investigative hormones (IAA,
GA3, BAP, ABA and ETH) enhanced RuBPCO activity and IAA was most stimulatory.
Various experiments show that phytohormones positively affect photosynthetic
processes under stress conditions. Soybeans exogenously treated with different plant
growth regulators under water stress had a noticeable effect on the chlorophyll
content, photosynthetic rate and PSII photochemical efficiency whereas under normal
conditions no significant difference between control and plants affected with
growth regulators was found (Mingcai et al., 2004). Analyzing the effect of ABA
and cytokinins on bean stomatal conductance, rates of transpiration and photosynthesis,
Pospiðilova J. (2003) reported that both growth regulators decreased net photosynthetic
rate, transpiration rate and stomatal conductance in sufficiently watered
plants when they were immersed to the solution with phytohormones (Pospiðilova,
2003).
Results of the present study demonstrated that particular CAHD concentrations,
which stimulated adventitious root formation, also increase bean photosynthetic
activity. As it is seen in Fig. 4, st-120 (0.05 mg·l -1 ) enhanced photochemical
quenching and was by 11% higher than in control plants. This parameter shows
the actual fraction of PSII reaction centers that are in open state (with re-oxidised
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